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Saturday, May 05, 2007

Necessary Existence, Truthmakers, and Modal Solipsism

This post developed out of some thoughts I had in response to the symposium on “The Contingency of Existence” at the Pacific APA convention in April, and also in response to Timothy Williamson’s paper “Necessary Existents”, which can be found here: <http://www.philosophy.ox.ac.uk/members/twilliamson/index.htm>. As I understand it, the problem with saying that a certain individual, say me, might not have existed is as follows: If I do not exist, then the proposition that I do not exist is true. If this proposition is true, however, it must exist. But if this proposition exists then so must I, for if I did not exist the proposition would have no subject to which it could attribute non-existence, and hence it could not assert my nonexistence. The proposition, if true, is false, and therefore it is false. The argument can be repeated for any individual, so we can conclude that the thesis of Necessary Existence is true: Anything which exists exists necessarily. I will not offer any support or criticism of this argument here; I will simply note that, the counterintuitiveness of its conclusion notwithstanding, there seems to be nothing obviously wrong with it. However, there is a different argument, which I formulate below, that threatens to turn this counterintuitive conclusion into something truly radical. I call this radical thesis “Modal Solipsism”. If Necessary Existence really carries this commitment, it is something we ought to reject if doing so is at all possible. I will argue, however, that the commitment to Modal Solipsism is illusory.

The argument goes like this: If Necessary Existence is true, any truthmaker which exists in any possible world exists in all. But a truthmaker for a proposition p is something such that, necessarily, if it exists then p is true. Consequently, since the truthmakers for every true proposition exist necessarily, every true proposition is necessarily true. Not a single thing could have been otherwise, for if it could, some proposition which is in fact true could have been false, and given the above supposition that is not possible. The thesis of Necessary Existence seems to collapse into Modal Solipsism: There’s just one possible world, and this is it!

Is there any way we can accept Necessary Existence and escape Modal Solipsism? I think there is, if we’re prepared to reject the above criterion on truthmakers. That is, we must reject the idea that, for every proposition p, a truthmaker for p is something such that, necessarily, if it exists then p is true. In other words, the existence of a truthmaker for p need not be sufficient for p’s truth. How can we cash this out?

The solution I propose depends on the idea that there is more to reality (and to truthmaking) than the simple existence of objects, either abstract or concrete. If there are at least two possible worlds which are exactly alike with respect to what exists in them, but which differ in respect to which objects exemplify which properties, these differences cannot be accounted for in terms of there being truthmakers which exist in one world but not in another. In such a scenario, what is the case is underdetermined by what exists. Existential propositions will have truthmakers, but we must look elsewhere for the truthmakers of non-existential ones.

States of affairs provide the way out, but only if we conceive of them abstractly, as Alvin Plantinga does: If we deny that there are states of affairs which do not obtain, then what is the case will once again coincide with what exists, and the thesis of Necessary Existence will commit us to Modal Solipsism. But if we hold that states of affairs obtain contingently and exist necessarily there is no problem. The possible worlds will differ only with respect to which states of affairs obtain, not with respect to what exists. As a first pass, we can say that it is the obtaining of a state of affairs which is the truthmaker for a non-existential proposition.

The above, however, is not quite right. As far as I can tell, a given state of affairs S and the state of affairs “S’s obtaining” are one and the same state of affairs. Thus, if p is a proposition which asserts that S obtains, the truthmaker for p is S itself, otherwise p would have no truthmaker at all. S will no doubt have different properties in those worlds in which it obtains than it has in those worlds in which it does not obtain, but the worlds in which it obtains have no additional existents which could serve as truthmakers for p only in those worlds. We must remember that everything which exists in one world exists in all. In consequence of this, S is the truthmaker for p whether S obtains or not. What we ought to say then, on this account, is that a truthmaker for a non-existential proposition p, in spite of its name, only makes p true if it obtains. Its bare existence is not enough. If the distinction between the existence of a state of affairs and its being the case survives scrutiny, we can hold that everything necessarily exists without holding that everything is necessarily true. Whatever plausibility Necessary Existence has need not be transmitted to Modal Solipsism.